allow to sync icons from free and pro package for custom FA versions

[Gummibeer]

fixes #30

The command has the old name as alias - that way this PR isn't breaking.

The command now also has two new options --free and --pro to enforce a specific FA package. The default will pick the one of both that is installed - preferring the pro one. So the default behavior stays the same.

• If you call artisan blade-fontawesome:sync-icons with the free set installed it will sync free ones.
• If you call artisan blade-fontawesome:sync-icons with the pro set installed it will sync pro ones.
• If you call artisan blade-fontawesome:sync-icons with the free and pro set installed it will sync pro ones.
• If you call artisan blade-fontawesome:sync-icons with nothing installed it will error.
• If you call artisan blade-fontawesome:sync-icons --pro with the pro set installed it will sync pro ones.
• If you call artisan blade-fontawesome:sync-icons --pro with the free set or nothing installed it will error.
• If you call artisan blade-fontawesome:sync-icons --free with the free set installed it will sync free ones.
• If you call artisan blade-fontawesome:sync-icons --free with the pro set or nothing installed it will error.

[Gummibeer]

Great! 🥳 Just a ping for the hacktoberfest-accepted label. 🙈😂